Is Cosmological Time Dilation real?

[PeterDonis]

How is c governed by the fine structure constant in the sense of; If it's "stronger" then is c faster?

On our current understanding, dimensionless constants like the fine structure constant are actually the more "fundamental" quantities; dimensionful quantities like $c$ are actually artifacts of our system of units (after all, we can always choose units to make $c = 1$). So it's not so much that increasing the fine structure constant makes the speed of light "faster", as that increasing the fine structure constant, which increases the strength of the electromagnetic interaction, changes the behavior of the things we use to measure how "fast" light travels.

In the case of johne618's proposed experiment (which I'll modify slightly to eliminate any issues with measuring time intervals at spatially separated locations), if we emit a beam of laser light that reflects off a mirror a distance $L$ away and comes back and is detected, and we count the number of atomic clock oscillations between the emission and detection of the beam, if $\alpha$ changes, that changes both the interaction strength that governs the atomic clock oscillations, *and* the interaction strength that governs the measuring tools we used to measure the distance $L$.

Heuristically, increasing $\alpha$ makes the atomic clock oscillations "faster" (electrons are pulled towards the nucleus more strongly, so they have to orbit faster to maintain a stable orbit), and it "shortens" the measuring tools (by strengthening the interactions that hold them together) that are used to determine $L$, and the two effects should cancel each other out, at least to a first approximation, which is why I said I didn't think this experiment would work anyway, because I don't think it would give different results even if the fine structure constant *did* change. (But, as I said, there are other ways to estimate what the fine structure constant was in the past.)

 

[PeterDonis]

I think that Peter Donis is right that your experiment seems to test changes in the fine structure constant.

Actually, I was saying that I don't think his experiment even tests that; I don't think its results would change even if the fine structure constant changed.

 

[nitsuj]

On our current understanding, dimensionless constants like the fine structure constant are actually the more "fundamental" quantities; dimensionful quantities like $c$ are actually artifacts of our system of units (after all, we can always choose units to make $c = 1$). So it's not so much that increasing the fine structure constant makes the speed of light "faster", as that increasing the fine structure constant, which increases the strength of the electromagnetic interaction, changes the behavior of the things we use to measure how "fast" light travels.

In the case of johne618's proposed experiment (which I'll modify slightly to eliminate any issues with measuring time intervals at spatially separated locations), if we emit a beam of laser light that reflects off a mirror a distance $L$ away and comes back and is detected, and we count the number of atomic clock oscillations between the emission and detection of the beam, if $\alpha$ changes, that changes both the interaction strength that governs the atomic clock oscillations, *and* the interaction strength that governs the measuring tools we used to measure the distance $L$.

Heuristically, increasing $\alpha$ makes the atomic clock oscillations "faster" (electrons are pulled towards the nucleus more strongly, so they have to orbit faster to maintain a stable orbit), and it "shortens" the measuring tools (by strengthening the interactions that hold them together) that are used to determine $L$, and the two effects should cancel each other out, at least to a first approximation, which is why I said I didn't think this experiment would work anyway, because I don't think it would give different results even if the fine structure constant *did* change. (But, as I said, there are other ways to estimate what the fine structure constant was in the past.)

Wow flippin' remarkable! Thanks for the clear explanation too.

 

[harrylin]

All the evidence that, for example, the fine structure constant has not changed significantly in the past few billion years, since the fine structure constant affects the frequency of atomic oscillations.

I still don't see how that that makes it detectable; and next you seem to also not see how:

[..]
Heuristically, increasing $\alpha$ makes the atomic clock oscillations "faster" (electrons are pulled towards the nucleus more strongly, so they have to orbit faster to maintain a stable orbit), and it "shortens" the measuring tools (by strengthening the interactions that hold them together) that are used to determine $L$, and the two effects should cancel each other out, at least to a first approximation, [..]
I don't think it would give different results even if the fine structure constant *did* change. (But, as I said, there are other ways to estimate what the fine structure constant was in the past.)

So I ask again: what other ways?

 

[PeterDonis]

So I ask again: what other ways?

Did you read the paper I linked to? It uses details about spectral lines to estimate what the fine structure constant was when the spectra were emitted.

The Usenet Physics FAQ also gives a brief overview with references:

http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/constants.html

 

[harrylin]

Did you read the paper I linked to? It uses details about spectral lines to estimate what the fine structure constant was when the spectra were emitted.

The Usenet Physics FAQ also gives a brief overview with references:

http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/constants.html

Ehm no, sorry: it's not clear to me why that constant would change with such a time dilation - but I may have missed it. In which post was that explained?

 

[PeterDonis]

Ehm no, sorry: it's not clear to me why that constant would change with such a time dilation - but I may have missed it. In which post was that explained?

Are you asking about why I think the fine structure constant would have to have changed over time if johne618's hypothesis were correct? I thought you were asking about how we can test for changes in the fine structure constant over time, since the test johne618 proposed does not work (at least, I don't think it works).

Johne618's hypothesis is that the observed redshift of very distant objects means that "the frequency of atomic systems increases with the scale factor a". The only way I can see for that to have any physical meaning is for the fine structure constant, which is the dimensionless constant that governs "the frequency of atomic systems", to depend on the scale factor. The dependence would have to be linear because the observed redshift is linear in the scale factor. Any such dependence is ruled out by 5 orders of magnitude by the tests in the links I gave.

 

[harrylin]

Are you asking about why I think the fine structure constant would have to have changed over time if johne618's hypothesis were correct? [..]

Johne618's hypothesis is that the observed redshift of very distant objects means that "the frequency of atomic systems increases with the scale factor a". The only way I can see for that to have any physical meaning is for the fine structure constant, which is the dimensionless constant that governs "the frequency of atomic systems", to depend on the scale factor. [..].

That doesn't necessarily follow, IMHO. If A is known to vary as function of B, then a change of A doesn't necessarily imply that B changed.

 

[PeterDonis]

That doesn't necessarily follow, IMHO. If A is known to vary as function of B, then a change of A doesn't necessarily imply that B changed.

What other physical meaning would you assign to "the frequency of atomic oscillations increases with the scale factor a"?

 

[harrylin]

What other physical meaning would you assign to "the frequency of atomic oscillations increases with the scale factor a"?

The size of the universe? That's what I guessed from "Universal scaling factor" and "expanding space".
Probably this is what he meant: https://en.wikipedia.org/wiki/Scale_factor_(Universe)

 

[PeterDonis]

The size of the universe?

I didn't ask what physical meaning you would assign to the scale factor; I agree that "the size of the universe" is as good a quick description of that as any (though there are issues with it, as with all descriptions in natural language of physical concepts that really require math for precise definition).

I asked what physical meaning you would assign to the specific hypothesis that "the frequency of atomic oscillations increases with the scale factor". Just telling me what the scale factor itself means doesn't answer that, particularly when the obvious meaning that you and I agree on for the scale factor has nothing to do with time (and therefore frequency), and everything to do with space (and therefore wavelength), which is precisely the interpretation that the OP was questioning.

 

[harrylin]

I didn't ask what physical meaning you would assign to the scale factor; I agree that "the size of the universe" is as good a quick description of that as any (though there are issues with it, as with all descriptions in natural language of physical concepts that really require math for precise definition).

I asked what physical meaning you would assign to the specific hypothesis that "the frequency of atomic oscillations increases with the scale factor". Just telling me what the scale factor itself means doesn't answer that, particularly when the obvious meaning that you and I agree on for the scale factor has nothing to do with time (and therefore frequency), and everything to do with space (and therefore wavelength), which is precisely the interpretation that the OP was questioning.

The same physical meaning as the one that the OP gave: that light that is coming from processes that happened a very long time ago will be redshifted as measured by us. The correlation that he suggested doesn't need to imply a causal effect between "space" and "time".

 

[PeterDonis]

The same physical meaning as the one that the OP gave: that light that is coming from processes that happened a very long time ago will be redshifted as measured by us.

But that just restates the observable; the OP claimed a particular interpretation of it as well. I'm not arguing that we don't observe cosmological redshifts; of course we do. I'm arguing that the OP's interpretation of *why* we observe them can't be right.

The correlation that he suggested doesn't need to imply a causal effect between "space" and "time".

Of course not; but the OP apparently thinks it does. So he must be using an interpretation that *does* imply such a correlation.

 

[harrylin]

[..] the OP apparently thinks it does. So he must be using an interpretation that *does* imply such a correlation.

You mean, not just a correlation, but a causal effect relation from one to the other? I didn't notice that - maybe I missed it. Let's wait for him to clarify that point, it's no use to discuss that without him!

 

[johne1618]

You mean, not just a correlation, but a causal effect relation from one to the other? I didn't notice that - maybe I missed it. Let's wait for him to clarify that point, it's no use to discuss that without him!

I've changed my mind!

I no longer think that atomic frequencies change with the Universal scale factor for an atomic system that stays at rest. Equivalently the proper time for a co-moving observer is always just the cosmological time.

However I think cosmological time dilation is a real effect but only occurs in the following situation. Clocks A and B are synchronized at one location. Clock B is transported by rocket ship to a distant location. One then waits a long time with the clocks separated by a co-moving distance. Then clock B is transported back to clock A. Clock A will have advanced further than clock B largely due to cosmological time dilation.

Is that right?

 

[Drakkith]

I've changed my mind!

I no longer think that atomic frequencies change with the Universal scale factor for an atomic system that stays at rest. Equivalently the proper time for a co-moving observer is always just the cosmological time.

However I think cosmological time dilation is a real effect but only occurs in the following situation. Clocks A and B are synchronized at one location. Clock B is transported by rocket ship to a distant location. One then waits a long time with the clocks separated by a co-moving distance. Then clock B is transported back to clock A. Clock A will have advanced further than clock B largely due to cosmological time dilation.

Is that right?

Nope. Clock B will be behind clock A, but purely because of relativistic time dilation due to traveling away and then back again via the rocket.